1. Field of the Invention
The present invention relates to an on-vehicle electronic control apparatus and, in particular, to an on-vehicle electronic control apparatus including a power circuit suitable to use a low power consumption type microprocessor having a standby open-circuit switch to supply a CPU drive current and a backup current for a RAM memory from a common power terminal.
2. Related Art
An on-vehicle electronic control apparatus is well known which includes plural constant-voltage power circuits in which a drive power voltage Vdd (e.g. DC 3.3 V) for an arithmetic circuit section cooperating with a non-volatile program memory or a volatile RAM memory is reduced compared to a power voltage Vcc (e.g. DC 5 V) for interface circuit, and a hold voltage Vup for battery backup is supplied to the RAM memory so that a microprocessor operates at a low power consumption and at a high speed.
For example, according to the following Patent Document 1, two types of DC 5 V power supplies that generate an output voltage Vad of high precision and small capacity for an analog sensor and an output voltage Vif of low precision and large capacity for on-off sensor are provided for an interface circuit with respect to a microprocessor, a DC 3.3 V power supply that generates an output voltage Vcp of low precision, low voltage and large capacity is provided for driving an arithmetic circuit section, a DC 3.3 V (or DC 2.8 V) power supply that generates an output voltage Vup of low precision, low voltage and micro capacity is provided for the backup of a RAM memory, and a DC 3.3 V power supply that generates an output voltage Vsb of low precision, low voltage and small capacity is provided for driving a combined control circuit section cooperating with the microprocessor.
Moreover, the constant-voltage power circuits that generate the output voltages Vad, Vif and Vcp are powered from an on-vehicle battery through an output contact of a power relay energized when a power switch is closed, the constant-voltage power circuit that generates the output voltage Vup is always powered from an on-vehicle battery regardless of an on-off operation of a power switch, and the constant-voltage power circuit that generates the output voltage Vsb is powered through an output contact of a power relay or is always powered from an on-vehicle battery according to the application thereof, so that the on-vehicle electronic control apparatus can detect failure of each constant-voltage power circuit as a whole.